Paul Nagelkerke

Inhibiting prepared and ongoing responses: Is there more than one kind of stopping?

Inhibiting movements has been investigated widely using the countermanding (stop signal) paradigm. Although it has been assumed that response inhibition, as measured by the countermanding task, generalizes to all forms of stopping, this has never been tested. In the present study, stopping performance in the countermanding paradigm was compared with stopping performance in a new paradigm in which a continuous-tracking task was used. Although stimulus presentations were matched across paradigms, the two tasks differed in the type of stopping required. In the countermanding paradigm, response inhibition latency was measuredprior to response execution—this is, it was inferred from the successful withholding of ago response. In the new paradigm, response inhibition was carried outafter response execution—that is, it was measured as the time to begin stopping a continuous tracking response. Results indicated that stopping latencies between the two paradigms were highly correlated, providing strong evidence that stopping an unexecuted response engages the same mechanisms as stopping an ongoing response.

Identifying visual–vestibular contributions during target-directed locomotion

The purpose of this experiment was to examine the potential interaction between visual and vestibular inputs as participants walked towards 1 of 3 targets located on a barrier 5m away. Visual and vestibular inputs were perturbed with displacing prisms and galvanic vestibular stimulation (GVS), respectively. For each target there were three vision conditions (no prisms, prisms left, and prisms right), and three GVS conditions (no GVS, anode left, and anode right). Participants were instructed to start with eyes closed, and to open the eyes at heel contact of the first step. GVS and target illumination were triggered by the first heel contact. This ensured that the upcoming visual condition and target were unknown and that both sensory perturbations occurred simultaneously. Lateral displacement was determined every 40 cm. Irrespective of target or direction, GVS or prism perturbation alone resulted in similar lateral deviations. When combined, the GVS and prism perturbations that had similar singular effects led to significantly larger deviations in the direction of the perturbations. The deviations were approximately equal to the sum of the single deviations indicating that the combined effects were additive. Conflicting GVS and prism perturbations led to significantly smaller deviations that were close to zero, indicating that opposite perturbations cancelled each other. These results show that when both visual and vestibular information remain important during task performance, the nervous system integrates the inputs equally.

Predictability Influences Stopping and Response Control

Using a continuous tracking task, the authors examined whether stopping is resistant to expectancies as well as whether it is a representative measure of response control. Participants controlled the speed of a moving marker by continuously adjusting their response force. Participants stopped their ongoing tracking in response to auditory signals on 25%, 50%, 75%, or 100% of trials. Stopping was contrasted with accelerating, in which participants accelerated the marker in response to the signals. In Experiment 1, on each trial participants either stopped or accelerated, allowing a trade-off between the two. In Experiments 2 and 3, participants only stopped or only accelerated, thus decreasing the likelihood of a trade-off. When a trade-off was possible, stopping was resistant to expectancies. However, with little or no trade-off, expectancies influenced stopping and accelerating similarly. These findings contrast with the established view that stopping is insensitive to expectancies. In addition, when trade-offs are prevented, these results confirm that stopping is representative of other response adjustment measures.

The use of computer interactive video in sport analysis

Abstract A computer-video interactive system is described that enables a trained observer to systematically record and view the behaviour of athletes performing within a team-sport competition. This system is designed to allow the recall of selected video instances from previously recorded athletic behaviours. In order to accomplish this form of analysis, a computerized recording system and a video cassette recording machine were combined using specialized hardware and software. A system for the analysis of field hockey is used to exemplify how the interaction of computers and video recorders can aid in the sport analysis process.

Measuring online volitional response control with a continuous tracking task

We present a new tracking task designed to measure elements of response control in particular types of response adjustments such as stopping. In this task, participants track a visual target by manually pressing on a force sensor to yield a trace of force over time. Hardware specifications are detailed, as is an algorithm for determining the latencies of response adjustments such as stopping. We illustrate the use of the task in two experiments. Experiment 1 explores the reliability of data produced by the task. Experiment 2 examines some of the issues that can be addressed using the new task. These results demonstrate the usefulness and potential of the task for gauging response control within the context of the stopping literature.

Compatibility effects in stopping and response initiation in a continuous tracking task

Two experiments explored stopping performance using a new stimulus–response compatibility effect spanning action initiation and stopping. Participants tracked a sometimes-moving, sometimes-stationary target by controlling the speed of a response marker via a force sensor. In the compatible condition, participants pressed the sensor in response to the target moving and stopped pressing in response to the target stopping. In the incompatible condition, participants stopped pressing in response to the target moving and initiated pressing in response to the target stopping. Response initiation and stopping were found to be faster under compatible than under incompatible conditions, regardless of whether compatible and incompatible trials were blocked or mixed. These findings indicate that stopping, like response initiation, is influenced by stimulus–response properties such as compatibility. This in turn suggests that stopping is governed by constraints similar to those of other behaviours.

Computer controlled video: an inexpensive IBM based system

Abstract This paper describes in detail an IBM based computer interactive video system that can be used in behavioural science research. This system operates in conjunction with an IBM XT (or compatible) and requires a circuit board to be resident within the computer. The system is designed to interact with a video cassette recorder (VCR) that has a 34 pin remote control outlet (some Sony and Panasonic AG and NV series). The interaction between the computer and VCR is outlined as well as the technical details of the circuit boards. In addition several software programs are given that demonstrate the control features of the circuit board.

An optical encoder and XY oscilloscope interface for the IBM PC

This paper outlines a prototype dual-purpose interface card for the IBM PC for use in research on motor learning and control. The card enables automatic interfacing for up to four angular optical encoders and presents high-speed visual data on an XY oscilloscope. In addition, it uses two single-chip microcontrollers with minimal external hardware, providing a more powerful instrument than is available in discrete hardware. Two microcontrollers operate independently of the experimental computer (IBM PC), using a common interface allowing the exchange of data. This interface card frees the experimental computer from the workload associated with optical encoders and high-speed XY displays, resulting in less complex experimental setups and data collection programs.